What you need to do is overwrite the existing Device Style Definitions in your drawings with your new Device styles. You can do this in Style Manager. To overwrite the device styles, follow these steps.
1. Open both your existing drawing and a drawing that contains your new styles (most likely your source dwg in your content folders).
2. Open Style Manager. You should see that both the files are listed on the left pane of the window.
3. Navigate to your Electrical Device Styles in you drawing with the new styles. They're located at Electrical Devices -> Device Styles.
4. Select the styles that you need to update. Drag and drop the styles into your existing drawing.
5. When prompted that the styles already exist in the drawing, choose to overwrite the existing styles.
This process should update all of your devices. You can do this sort of procedure with a lot of style-based items, so keep it in mind in the future.
Cheers,
Kyle B
ABS Product Support
Kyle Bernhardt
Director
Building Design Strategy
Autodesk, Inc.